The subject of the present invention is a motorized reduction gear intended for functional equipment of a vehicle, such as a window lifter, sunroof, etc.
Such a motorized reduction gear comprises a rotor provided with a rotor shaft bearing a commutator, and a reduction gearbox containing a gearwheel engaged with a worm belonging to the shaft. In order that the number of shaft rotations can be counted, a magnetic ring is mounted on the shaft, between the commutator and a rolling bearing placed in the gearbox. This mounting is achieved by force (a “press fit”) using longitudinal notches made on the shaft, which hold the ring in place.
This arrangement therefore requires two pieces to be assembled on the motorized reduction gear assembly lines. It is found that, after a certain time in service, the retention of the ring on the shaft becomes insecure, the ring having a tendency to detach from the shaft, which may in certain cases even lead to the destruction of this magnetic ring. This defective retention of the ring on the shaft may arise from a fault in the alignment of the ring with the shaft during the assembly operation, and, where appropriate, from the fact that the internal diameter of the magnetic ring is too small.
The aim of the invention is therefore to provide a motorized reduction gear in which the magnetic ring for counting the shaft rotation rate is attached to the shaft in a way which is more reliable over time.